Much of the sweet corn that is grown for human consumption is removed from the cob for canning and freezing while the corn kernels are still "green". Corn is considered green when the kernels are still moist and soft and have not matured into seed.
One type of machine that is used in the food processing industry for this purpose is shown and described in Kerr, U.S. Pat. No. 2,787,273. This machine uses six cutting instruments with curved cutting edges that are generally positioned around a circle and around an adjustable aperture. The cutting instruments project forward from the aperture, and together with the aperture form what is known in the industry as an "iris". Ears of corn are shucked and then are fed endwise through the iris--small end first.
The corn cutting instruments or "knives" are unitary or integral parts that are installed in the cutting machine. Each knife has a planar arm that reaches inward towards the center of a cylindrical cutting head where the iris is located. The arm is located in a plane transverse to the longitudinal axis of each ear fed through the aperture of the iris. At the inner or working end of the arm, the knife turns parallel to the ear, and presents a blade of some width that is formed concave relative to the ear. It is known that the blade is angled upward, from heel to toe, at a certain "cob angle" from the longitudinal axis of the ear. This allows the blade to ride up the taper of the cob from the small end to the large end as the kernels are cut off.
At its free end or toe, which meets the oncoming ear of corn, the blade is sharpened to form a curved cutting edge. The curved cutting edge is more complex than a simple arcuate portion of a circle. The bottom of the blade is made concave in an arc related to a spiral cutting path around the cob. The bottom of the blade also controls the depth of the cut so that the kernels are severed at a selected height relative to the pithy part of the cob.
It is also known that the cutting edge should attain a specified oblique angle, which is seen in a plane that is tangent to a midpoint of curvature for the cutting edge. It is also known that the knives of the prior art presented an edge forming a specified "edge angle" between the tap surface of the blade and the bottom surface of the blade which rode along the ear.
In operation of the machine, the six blades are carried by a rotating cutting head and are spun around the ear as it passes through the iris. If one of the knives cuts too deeply, a spiral gouge will be seen on the stripped cob. This is one of the observations of the cob that is indicative of corn cutting inefficiency. The geometry of the cutting edges relative to the corn kernels and the corn cob must be maintained to assure a satisfactory yield of corn kernels.
After a period of use, the cutting edges become dull to the point that the yield of properly cut kernels drops. The current maintenance procedure is to remove the knives--only a small part of which is occupied by the cutting edges--and resharpen the cutting edges. This resharpening requires special equipment provided by the machine manufacturer and considerable labor for the many instances when resharpening is necessary. The machine manufacturer also recommends that periodically the knives be returned to a manufactureroperated, central sharpening facility, where the knives can be rehoned, reground and generally returned to an acceptable cutting profile. Even with these procedures, there is a further disadvantage that the blade becomes shorter with repeated resharpening and rehoning, and the original cutting knife condition cannot be fully restored.